The present disclosure relates to a nonaqueous electrolyte secondary battery.
Among nonaqueous electrolyte batteries, a lithium ion secondary battery is rapidly developing as a power source of portable electronic appliances such as a mobile phone and a portable personal computer. In the power source for such a portable electronic appliance, an energy density, namely an energy storage capacity per unit volume is the most necessary characteristic, and how long the portable appliance can be used attracts interest.
JP-A-2004-22336 discloses that a lithium secondary battery having not only excellent characteristics in energy density, electromotive force and the like but excellent cycle life and safety is obtained using an electrolytic solution in which a sulfonic anhydride is contained in an aprotic organic solvent.
JP-A-2002-134170 discloses that in a nonaqueous electrolytic solution secondary battery using a cobalt-containing positive electrode active material, when a compound capable of forming a complex with cobalt is added to an electrolytic solution, a cobalt ion eluted in the electrolytic solution is stabilized, and its deposition on a negative electrode is suppressed, thereby reducing a reaction area of the negative electrode and suppressing the generation of a gas to be caused due to a catalytic reaction of cobalt; thus, a nonaqueous electrolytic solution secondary battery which is excellent in high-temperature storage characteristic and high-temperature charge and discharge cycle characteristic can be provided.
However, for example, when a portable personal computer is allowed to stand in a continuously connected state to a power source, the battery within a battery pack is exposed in a charged state (floating state), and the battery capacity is abruptly deteriorated. This is caused due to the fact that cobalt or the like which is contained in the positive electrode active material is easily eluted in an oxidizing atmosphere, and at the same time when the interfacial resistance increases, the capacity is lowered by a change in the layered structure. Furthermore, an increase in the circumferential temperature following drive of the portable personal computer is a factor in acceleration of the deterioration.
Also, there is involved a problem that when the battery is exposed in a charged state (floating state), a gas is generated due to a reaction between the electrolytic solution and the positive electrode active material, thereby causing blister of the battery, resulting in a lowering of the quality.
As reform measures, there is a technology in which even when Co is eluted from a lithium cobalt complex oxide, the battery is stabilized by an additive of the electrolytic solution, thereby avoiding an adverse influence against the negative electrode. However, though the adverse influence against the negative electrode to be caused due to the elution of Co can be avoided, the positive electrode resistance increases by a change in the positive electrode structure, and the capacity is deteriorated. Namely, a battery with high reliability is not obtainable unless the own elution of Co is suppressed. A phenomenon of the elution of a metal ion is common in not only the lithium cobalt complex oxide but nickel oxides, manganese oxides, iron olivine phosphates and so on.
That is, a nonaqueous electrolyte secondary battery which is further excellent in a floating characteristic is being desired.
It is therefore desirable to provide a nonaqueous electrolyte secondary battery which is excellent in a floating characteristic.